1. Field of the Invention
The present invention relates to a method for providing surface texturing of an aluminum sheet, a substrate for a lithographic plate, and to a lithographic plate. In particular, the invention relates to a method for providing concavo-convex texturing to an aluminum sheet used for, for example, producing a substrate for a lithographic plate by using an embossing form having a concavo-convex pattern formed on its surface and transferring the concavo-convex pattern of the embossing form to at least one surface of the aluminum sheet, particularly to a technique for forming a concavo-convex pattern on the embossing form.
2. Related Art
Articles which are produced by using an aluminum sheet as a substrate and providing surface texturing of the substrate surface so as to form a concavo-convex pattern on the same include, for example, substrates for lithographic plates and an aluminum decorative laminate.
As a method for providing surface texturing of an aluminum sheet, in more particular, a method for providing concavo-convex texturing, such as embossing, to the surface of an aluminum sheet for producing a substrate for a lithographic plate by rolling the aluminum sheet with a transferring roll having concaves or convexes formed on its surface, Japanese Patent Application Laid-open No. 60-36196 describes a method for providing embossing to the surface of an aluminum sheet using a pressure roll whose steel roll has its surface shot blasted. Japanese Patent Application Laid-open No. 62-25094 describes a method for providing embossing to the surface of an aluminum sheet by rolling the aluminum sheet using a steel roll which has undergone honing (Ra=0.5 to 1.5 μm and 500/mm2 or more concaves or convexes of 0.6 μm or more deep) with a rolling reduction of 2 to 20%. Further, Japanese Patent Application Laid-open No. 62-111792 describes a method for providing embossing to the surface of an aluminum sheet by rolling the aluminum sheet using a roll which has undergone chemical etching or honing (Ra=0.5 to 1.5 μm, 500/mm2 or more concaves or convexes of 0.6 μm or more deep) with a reduction of 2 to 20%. Still further, Japanese Patent Application Laid-open No. 62-218189 describes a method for providing embossing to an aluminum sheet by rolling the aluminum sheet using a roll having concaves or convexes formed on its surface by electrical discharge machining (Ra=0.7 to 1.7 μm, 500/mm2 or more concaves or convexes of 0.6 μm or more deep) with a reduction of 2 to 20%.
Techniques for providing surface texturing of metal sheets include the following ones, though these are intended to provide surface texturing of an aluminum sheet for producing a substrate for a lithographic plate. For example, Japanese Patent Application Laid-open No. 10-99905 describes a method for producing an aluminum or aluminum alloy sheet of an intended thickness by cold rolling, wherein the rolling operation of the final pass is performed using a pressure roll whose surface is coated with hard chromium plating 3 to 12 μm thick and has a center-line average roughness in the direction of the roll axis, Ra, of 0.2 to 0.7 μm, so as to produce a less anisotropic aluminum or aluminum alloy sheet.
Japanese Patent Application Laid-open No. 10-328705 describes a method for producing an aluminum or aluminum alloy sheet by cold rolling, wherein the cold rolling operations are performed using a work roll for rolling whose surface is coated with hard chromium plating 3 to 12 μm, has surface projections formed on the chromium plate coating that satisfy the following conditions: h/D≦0.2 and h≦1.5−(2.5 h/D) (where h represents the height of the surface projections and D the diameter of the circumscribed circle of plane of the same), and has a center-line average roughness in the direction of the roll axis, Ra, of 0.2 to 0.7 μm.
Japanese Patent Application Laid-open No. 10-259499 describes a method for roughening the surface of stainless steel sheet, wherein roughening was performed by applying alternating electrolysis to the stainless steel surface in an aqueous solution of ferric chloride to produce stainless steel sheet superior in adhesion to various covering materials. Further, Japanese Patent Application Laid-open No. 2003-3300 describes a method for roughening the surface of steel sheets other than stainless steel, such as ordinary steel or special steel sheets, wherein roughening is performed by using the steel sheet as an anode and subjecting the same to anodic electrolysis at a current density of 50 to 150 A/dm2 while allowing oxygen bubbles to occur on the surface of the steel sheet, so as to enhance the adhesion of the steel to coated films or adhesives.
In the meantime, an aluminum decorative laminate is being used as members of cars, air conditioners, TV sets or radios with the object mainly of making such products more lightweight and providing the same with aesthetics and nobleness which other metals such as iron cannot provide. Or they are being used for interior decoration for aesthetic purpose. The main objectives of forming a concavo-convex pattern on an aluminum decorative laminate are: first to modify the glossiness and second to enhance paint adhesion when applying painting to the decorative laminates. Normally, an aluminum decorative laminate have been produced by rolling aluminum sheets using a transfer roll whose surface is provided with a concavo-convex pattern in relief by etching or engraving.